1. Field of the Invention
The present invention relates to grain milling generally, and more particularly, to an improved differential corn milling process.
2. Description of Related Art
In a conventional corn milling process, corn kernels are cleaned, tempered, and then sent to a degerminator, which attempts to remove the germ from each kernel without substantially grinding the germ. The corn particles exiting the degerminator are separated into “tail” and “thru” streams, the former being relatively rich in endosperm and the latter being relatively rich in bran and germ. Each stream is then preferably passed through aspirators for bran removal and gravity tables to achieve further sorting of each stream by particle density.
Next, each stream is passed through a series of differential roller mills and sieves to grind and separate the corn particles within each stream to a desired size and purity. Typically, there are two series of differential roller mills, one for the endosperm rich stream (i.e. the break rollers) and one for the germ rich stream (i.e. the germ rollers). Each series consists of successive roller mills designed to gradually reduce endosperm particle size. Each roller mill consists of a pair of counter-rotating rollers which rotate at different speeds and have corrugations designed to grind the endosperm particles. Typically, the germ rollers have a lower roll speed differential than the break rollers in order to reduce grinding and abrasion on the relatively fragile germ.
The first roller mill in each series typically has relatively large corrugations (e.g. approximately 6 corrugations per inch) and the final roller mills in each series typically have relatively small corrugations (e.g. approximately 16-24 corrugations per inch). Relatively large particles from the gravity tables go to the first break or germ rollers, respectively, while smaller particles go to subsequent break or germ rollers. The particles are ground, separated, and re-ground until the desired separation and particle size is achieved. This gradual reduction process subjects corn kernels to multiple grinding and separating steps which can cause undesirable degradation of the germ stream. Further, the process does not separate all of the recoverable germ, and the oil contained therein, from the endosperm stream.
The assignee of the present application owns four patents directed toward a revolutionary corn milling process and degerminator invented by R. James Giguere, which eliminates many of the conventional corn milling steps that are described above: U.S. Pat. No. 4,189,503; U.S. Pat. No. 4,301,183; U.S. Pat. No. 4,365,546; and U.S. Pat. No. 5,250,313, all of which are incorporated by reference herein. According to the process described in these patents, corn kernels preferably are first fractured in a degerminator having opposed corrugated surfaces that crush the kernels from their thin edges to separate the germ and endosperm without damaging the germ. The fractured particles exiting the degerminator are then sent to a break roll having relatively fine corrugations of the type that normally characterizes the end of a differential milling process. The rollers are spaced apart a distance to grind the endosperm portion of the kernels without reducing the size of the germ. The stream exiting the break roll is then passed through sieves and may be ground further until a desired size and purity is achieved.
The assignee of the present application also previously developed the following corn milling process which is similar to the process described in the assignee's above described patents. According to this process corn kernels are first fractured in a pre-break mill or degerminator. The fractured corn particles are then passed through a break roller mill of the type that normally characterizes the end of a differential corn milling process (i.e. the roller corrugations are relatively small). The differential roll speed for the roller mill is no less than 1.6:1 as it was believed that any lower differential would not sufficiently grind the endosperm of the kernels. Sieves are then used to separate the particles into respective germ and endosperm streams. The grinding and separating steps are preferably repeated until the germ and endosperm are sufficiently separated. While the assignee of the present invention's previous processes have proven to be advantageous over the conventional process using two series of successive roller mills, there is room for further improvement in germ and endosperm separation.